There has been conventionally a contact holding sheet provided with a light guide, for example, as disclosed in JP 9-198902A and JP 2001-028220A. Small switches that are built in a cellular phone and other portable electronic devices are configured by dome-shaped movable contacts. Each of the movable contacts has a diameter of around 2 to 6 mm and fixed contacts that are opposed to the movable contacts. The movable contacts are held by the holding sheet. The fixed contacts are built in a substrate and opposed to the movable contacts.
In a state where the switches are built in the portable electronic devices, since the operation of switches is implemented by pushing central portions of the movable contacts, protrusions made of resin are formed on the holding sheet, and apexes of the protrusions are pushed to displace the movable contacts, thereby causing the movable contacts and the fixed contacts to be electrically brought into contact with each other. When the movable contacts come in contact with or separate from the fixed contacts, the switches are turned ON or OFF.
Meanwhile, the light guide made of a transparent film, and so forth is disposed between switch operation portions and the holding sheet for illuminating the switch operation portions. When the switches are operated, the light guide strikes against the protrusions made of resin, and cracks are liable to be generated in the light guide when implementing the life test of the switches, thereby causing a problem with durability.